1) Field of the Invention
The present invention relates to the joining of structural members and, more particularly, to a system and method for adjustably supporting and joining structural members using heads adjustably mounted on gantries.
2) Description of Related Art
Certain structural parts have conventionally been manufactured by joining a number of preformed structural members. For example, in the aircraft industry, wings are often manufactured by forming, and then joining, one or more skins and stringers. The skins, which are typically large and thin, form the outer contoured airfoil of the wing, and the stringers are joined to the skin to strengthen and stiffen the skins. According to one conventional manufacturing process, the skins and stringers are assembled in place in specially shaped fixtures and clamped therein with straps, which hold the skins and stringers in a desired configuration. Holes are then drilled through the skins and stringers, and some or all of the members are then removed from the fixture so that the holes can be deburred and metal chips or other debris can be removed from between the members. Sealant is then typically applied to the stringers, the members are again positioned in the fixtures, and temporary fasteners are installed to join the members. The assembled members are then brought to a workstation where operators remove the temporary fasteners and install permanent fasteners.
According to this conventional method, the structural members typically must be moved several times during assembly. For example, if the skins and/or stringers are not removed from the fixtures for cleaning after the holes are drilled, debris introduced between the members during drilling can damage the parts or impair the effectiveness of the joint and the finished wing. Thus, the process is time-consuming and labor intensive. Further, the fixtures, which must be shaped according to the particular members that are to be joined, add to the cost of manufacture. Additionally, sufficient factory space is required for moving and processing the members, and special equipment may be required for moving the members if they are large, heavy, or subject to being damaged.
For small structural members, the holes can sometimes be drilled before the members are assembled in the fixture, e.g., during the manufacture of the individual members. However, for members that are large, complex, or formed of certain materials, it can be difficult or impossible to predict the precise placement of the holes. For example, for long skins and stringers, thermal expansion or contraction of the members may be nonuniform throughout each member or between different members. If the holes are formed during manufacture of the members, the corresponding holes of the different members may not properly align during assembly. Therefore, the fixtures are used to align the members while the holes are formed.
Thus, there exists a need for an apparatus and method for joining structural members, including members that are large, heavy, complex, or made of various materials, for example, aluminum skins and stringers that are joined to form long aircraft wings. The apparatus should be adaptable for use with different structural members and preferably should not require an undue amount of factory space. Also, the method should not require excessive time or effort for joining the structural members.